A “systemic margin call” may cost Wall Street banks $325 billion of capital because of deteriorating subprime U.S. mortgages, according to a report released late last Friday by JPMorgan Chase.

Last week, the Carlyle Group’s mortgage fund failed to meet $37 million in margin calls and Thornburg Mortgage failed to meet a margin call of nearly $30 million.

According to the JPMorgan Chase report: “A systemic credit crunch is underway, driven primarily by bank writedowns for subprime mortgages … We would characterize this situation as a systemic margin call.”

“There is real risk of a trap door opening up — just as it did beneath the dollar after Bernanke went to Congress,” says Justice Litle.

“The real problem with all this credit crunch mess is one of uncertainty. No one knows just how deep the rabbit hole goes. Multiple attempts to bottom pick have resulted in failure. And for a number of high-profile hedge funds, that failure has been final.”